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Geopolymers: Promising Materials For Underground Applications
Emergence of alternative cements
Alternative cements (non-Portland cement based) have been around for about a century. Among these, alkali activated cements are of special importance. Reactions between alkalis and iron blast furnace slag were observed as early as the 1930s. During the 1960s, Zeolite A was prepared by reacting kaolinite with concentrated sodium hydroxide solutions. In 1972, water-resistant ceramic tiles were made without firing in reactions of kaolinite with alkaline solutions. It was in that same year, during the aftermath of a series of catastrophic fires in France, that scientist Joseph Davidovits, while researching noncombustible plastics and inorganic polymers, developed a process based on geosynthesis principles, which produced a “man-made” rock which he christened as “geopolymer.”
Although the term geopolymer and even the more scientific term “polysialate” are not universally recognized, Davidovits can be credited with the invention of geopolymer chemistry. Since then, geopolymer related research spread around the world, especially in countries like Spain, the Czech Republic and Australia with the latter being home to many geopolymer-related engineering contributions and the first commercial geopolymer products. The United States caught the ‘geopolymer fever’ relatively late, but has been ‘catching up’ since the early 2000s and can now be considered second only to Australia in terms of geopolymer research.
Even though early geopolymer formulations were mostly based in metakaolin, a calcined product from kaolin clay due to its high purity level and controlled properties, a significant commercial interest in geopolymer materials arose when it was discovered that fly ash, a byproduct of coal combustion, could also be used as an effective precursor. This discovery enabled the mass production of geopolymer by making use of the vast available supply of fly ash, helping to address two important environmental challenges, fly ash landfilling and CO2 emissions related to the production of Portland cement.